Effective diagnosis, treatment, and prevention of alcoholism and alcohol-related problems require accurate noninvasive measurement of blood alcohol concentration (BAC). Semiconductor sensors are widely used in breatholyzers owing to their high sensitivity, durability, small size, and low cost. But they respond to many common gases, preventing selective ethanol measurement. The proposed research overcomes this problem by merging microprocessor and sensor technologies for low-cost yet highly accurate ethanol measurement. Phase 1 research demonstrates feasibility of the technique for selective alcohol measurement by characterizing the responses of presently available semiconductor sensors to ethanol, humidity and representative interferences, by developing computer software to deconvolve these responses to selectively measure ethanol, and by determining the technique's robustness with respect to the interferences. In Phase 2 sensor materials will be optimized for portability, minimal power consumption, and detection accurary in order to microfabricate a single-chip sensor array suited for low-cost breatholyzers. Successful research will result in simple, rugged, pocket-sized breatholyzers that comprise a microfabricated single-chip gas-analysis probe and a low-cost microcomputer. These appliance instruments may be applied to chemical verification of treatment compliance, consumer self-evaluation of degree of intoxication, ignition locks for automobiles, and use by law enforcement agencies.